Crank mechanism and machines, especially engines, using same

ABSTRACT

An eccentric crank mechanism which communicates motion between a reciprocating piston and a rotary shaft comprising a crank pin having a connecting rod of the piston concentrically journaled thereon. The crank pin has an eccentric motion profile relative to the axis of the rotary shaft, the eccentric motion profile being controlled by a driving connection between a stator and a rotor which carries the crank pin. The rotary motion of the rotor and the rotary shaft is communicated one to the other by a journaled connection between the rotor and an eccentric journal of the rotary shaft. The driving connection comprises toothed grooving. The profile of the stator and rotor determines the eccentric motion profile.

DESCRIPTION

The present invention relates to a crank mechanism communicating motionbetween a reciprocating piston and a rotary shaft and to its applicationto machines, including all reciprocating prime movers such as heatengines, steam engines, compressors and expanders, which embody linearto rotary motion in their crank mechanisms and with particularapplication to internal combustion engines.

Reciprocating piston type prime movers have a slidable piston connectedto a crank pin of a crank shaft to compress or expand the gas (or othertype of fluid) in order to absorb or create energy or convert energyfrom one form to another. With the existing type of crank mechanism thecrank pin rotates concentrically with the axis of the crank shaft andthe performance characteristics are inextricably related to thegeometric principles of such a crank shaft configuration. Whilst muchhas been achieved by science and technology to improve the performancecharacteristics of such prime movers no attention appears to have beengiven to improving performance by changing the crank mechanism. Thepresent invention when incorporated in such machines aims at achievingradical performance improvements, for example increased thermalefficiency with internal combustion engines, without discarding all thathas been achieved to date.

Accordingly, one aspect of the present invention provides a crankmechanism communicating motion between a reciprocating piston and arotary shaft, comprising a crank pin having journalled thereon aconnecting rod of the piston, and wherein the crank pin has an eccentricmotion profile relative to the axis of the rotary shaft, the eccentricmotion profile being controlled by a driving connection between a statorand a rotor carrying the crank pin, and wherein rotary motion of therotor and the rotary shaft is communicated one to the other by ajournalled connection between the rotor and an eccentric journal of therotary shaft.

Another aspect of the invention provides a machine incorporating theafore-described crank mechanism. Where the machine is of the type whichconverts linear to rotary motion, such as an internal combustion engine,the afore-described rotary shaft is an output shaft to which rotarymotion is communicated from the rotor by way of the journalledconnection. A particular advantage of the use of the described crankmechanism in an internal combustion engine is that it enables therelationship between the thermodynamic cycle and the output torque to bevaried. In a conventional engine they cannot be varied in relation toone another. Where the machine is of the type which converts rotarymotion to linear motion, the rotary shaft is an input shaft whichcommunicates rotary motion to the rotor by way of the journalledconnection.

In converting linear to rotary motion (and vice versa), the eccentricmotion profile of the crank pin can exploit various geometricconfigurations to improve prime mover performance characteristics. Suchgeometric configurations can embody various combinations of stator/rotorshapes such as a circle rotating on a circle, a circle rotating on aelliptical/parabolic profile, tri-lobed and quad-lobed profiles invarious combinations. Furthermore the relative positions of stator androtor can be off-set in relation to each other for the further finetuning of performance aspects. Asymmetric configurations are alsocapable of being exploited. For construction in which the distance ofthe driving connections of the rotor and stator are variable relative tothe rotary shaft axis, a single piece rotary shaft would be expected tobe replaced by at least a two-piece construction accommodating relativeradial movement between the rotary shaft and its eccentric journal. As aresult the relative motion of the piston to the rotary shaft(conventionally the crank shaft) is therefore radically different fromall modern day prime movers enabling significant improvements inperformance characteristics of the machine to be achieved.

In one embodiment a geared connection is provided between the rotor andthe stator by for example an external gear on the stator and an internalgear configuration on the rotor. The rotary shaft is journalled forrotation with respect to the stator.

The crank mechanism has applications to single and multi-cylindermachine configurations.

The present invention will now be described further, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional view on X--X of FIG. 2 showing oneembodiment of crank mechanism according to the invention,

FIG. 2 is a section on Y--Y of FIG. 1 and including piston andconnecting rod detail,

FIG. 3a to 3d give examples of the crank pin motion profile fordifferent configurations of rotor and stator,

FIG. 4a is a side view of one embodiment of rotor for a multi-cylinderapplication,

FIG. 4b is an end view of the rotor on A--A of FIG. 4a to a reducedscale,

FIG. 5a is a side view of an alternative embodiment of rotor for amulti-cylinder application, and

FIG. 5b is an end view on B--B of FIG. 5 to a reduced scale.

Referring firstly to FIGS. 1 and 2, the invention is described by way ofexample with reference to a single cylinder application and illustratesa piston 1 received for reciprocating motion, denoted by double-headedarrow R, in a cylinder bore (not shown). The piston has a connecting rod3 journalled at one end to the piston and at the other to a crank pin 9.The crank pin is carried by a rotor 7 which in the illustratedembodiment has an internal gear at 13 having a uniform pitch circlediameter and arranged for geared connection with a stator 11 having amating gear configuration 14 also of constant pitch circle diameter inthe illustrated embodiment. Also illustrated is a rotary shaft or crankshaft 5 journalled for rotation about an axis 5a. One bearing forsupporting the crank shaft rotatably is shown at 15. Additional bearingsmay be required. In the illustrated embodiment the pitch circle diameterof teeth 14 is concentric with the axis 5a of the crank shaft. Therotary shaft has an eccentric journal part 19 on which the rotor 7 isjournalled by way of bearing 17 which is interposed between the externalsurface of the eccentric journal 19 and an internal cylindrical surface16 of the rotor.

The eccentric crank mechanism described above has the effect ofmodifying the movement profile of the piston compared with the simpleharmonic motion which the piston would have if the crank pin movedconcentrically with the crank shaft axis. In operation the rotor 7 willmove around the stator 11 by virtue of the geared connection 13, 14producing an eccentricity in the movement of the crank pin 9 instead ofthe normal circular rotation as with the normal slider crank mechanism.The motion of the rotor is constrained by the connection with the rotaryshaft at the journalled connection 17 and since its rotational axis 5ais fixed it serves to control the point at which engagement is madebetween the gears 13 and 14 during the rotation of the rotary shaft.Whilst the journalled connection 17 determines the relative radialposition of the rotor 7 it does not determine its relativecircumferential position. This is determined by the geared connection13, 14 and thus the output shaft can rotate at different speeds to therotor 7. Typically the output shaft rotates faster than the rotor. Therelative speed will depend on the geometric ratios of gears 13 and 14.

In applying the invention to a machine of the type which requires rotarymotion to be converted to linear motion, the rotary motion of the rotaryshaft is transmitted to the rotor by the journalled connection, whilstthe connection of the rotor with the stator prescribes the nature of thelinear motion at the piston. Where the invention is applied to a machineof the type which requires linear motion to be converted to rotarymotion, such as the internal combustion engine which is the preferredapplication of the described crank mechanism, the rotary motion of therotor is transmitted to the rotary shaft by the journalled connection.

FIG. 3a illustrates the crank pin motion profile x for the case of astator 11 having cylindrical external gearing (ie. of a constantdiameter) and mating with a rotor 7 having internal gearing of constantdiameter. The loci is the axis of the crank pin for a specific radialand circumferential position relative to the rotor configuration. As hasbeen mentioned above uniform pitch circle diameters of gears 13 or 14can be replaced by more complex shapes.

FIGS. 3b, 3c and 3d illustrate the crank pin motion profile x for otherconfigurations of stator 11 and rotor 7. More particularly, FIG. 3bshows a stator having an elliptical configuration mating with a rotorhaving a cylindrical configuration for the case where the relativeposition of the stator to the rotor is as shown at say top dead centreof the piston. FIG. 3c illustrates the motion profile for a rotor havingan approximately triangular shaped geared chamber rotating on anelliptical stator.

Finally, FIG. 3d shows the triangular shaped gear chamber of FIG. 3crotating on a quad-lobed stator and the resulting elliptical motionprofile. These are examples only and other configurations orcombinations could be arrived at to achieve the desired motion profile.In all cases a different motion profile is achieved by changing thepoint of meshing of the stator and rotor relative to top dead centre.Further changes can be produced by off-setting the rotational axis ofthe rotor and stator.

FIGS. 4a and 4b illustrate how the crank mechanism of the invention canbe utilised in multi-cylinder applications. The illustrated embodimentis for a 2 cylinder 180° configuration, but it could easily be adaptedto a flat four. The rectangular dotted outline 20 denotes a constructionequivalent to FIG. 1 described previously and only the rotor 7 and crankpin 9 are shown outlined. In order to adapt for multi-cylinders, therotor is modified to provide an additional crank pin 9' to receive aconnecting rod of an associated piston. This crank pin is connected tothe existing crank pin by waxy of a crank web 21 and in the illustratedembodiment spaced 180° relative to the axis 5a. Crank pin 9' is shownconnected to rotor 7'. Dotted outline 20' which may also be constructedas the equivalent of FIG. 1 but in mirror image, although generally onlyone rotary shaft is required.

FIGS. 5a and 5b illustrate how the crank mechanism can be applied to a 3or 6 cylinder embodiment. Again dotted outline 20 represents aconstruction equivalent to FIG. 1 and in this instance the crank pin 9connects with a first crank web 21' having crank pin 9' set at 120° fromthe pin 9 and this connects with a second crank web 21" spaced a further120°. This crank pin 9" is shown connecting with a rotor-like part 7 andwithin dotted outline 20" which may correspond to the construction ofFIG. 1 but in mirror image. The additional crank pins receive respectiveconnecting rods of associated pistons.

What is claimed is:
 1. A machine comprising: a stator; a rotary shafthaving an eccentric journal and an axis of rotation; a rotor carried bythe eccentric journal of the rotary shaft such that rotary motion istransferred between the rotor and the rotary shaft, the rotor beingconnected to the stator for communicating a driving force therebetween;a crank pin carried by the rotor, the crank pin having an eccentricmotion profile relative to the axis of the rotary shaft when the rotoris driven by the connection between the rotor and stator; areciprocating piston; and a connecting rod having one end and an otherend, the piston being carried on the one end and the other end beingconcentrically journaled on the crank pin such that motion iscommunicated between the piston and the rotary shaft.
 2. A machineaccording to claim 1 of the type which converts reciprocally linearmotion to rotary motion the rotary shaft being an output shaft to whichrotary motion is communicated from the rotor by way of the journaledconnection between the rotor and the rotary shaft.
 3. A machineaccording to claim 1 wherein the stator and the rotor each have acircular shape.
 4. A machine according to claim 1 of the type whichconverts rotary motion to linear motion, the rotary shaft being an inputshaft which communicates rotary motion to the rotor by way of thejournaled connection between the rotor and the rotary shaft.
 5. Amachine according to claim 1 wherein the driving connection between therotor and the stator is a toothed gear connection.
 6. A machineaccording to claim 1 wherein the driving connection of at least one ofthe stator or the rotor is asymmetric.
 7. A machine according to claim 1wherein the eccentric motion profile of the crank-pin has anepi-trochoid trajectory or a hybrid epi-trochoid trajectory.
 8. Amachine according to claim 1 wherein the relative positions of thestator and the rotor are off-set in relation to each other.
 9. Areciprocating piston machine comprising: an annular stator; a rotaryshaft having an eccentric journal and an axis of rotation, the rotaryshaft being rotatably mounted with respect to the annular stator; anannular rotor rotatably mounted on the eccentric journal andinterengaged with the stator for communicating a driving forcetherebetween; a crank pin disposed on the rotor, the crank pin having aneccentric motion profile relative to the axis of the rotary shaft whenthe rotor is rotated by the interengagement of the rotor and the stator;a connecting rod having one end and an other end, the other end beingconcentrically journaled on the crank pin; a reciprocating piston, thepiston being carried on the one end of the connecting rod such thatmotion is communicated between the piston and the rotary shaft.
 10. Thereciprocating piston machine of claim 9 wherein the rotor has an innercircumferential surface and the stator has an outer circumferentialsurface, the outer surface of the stator and the inner surface of therotor being interengaged for transmitting the driving forcetherebetween.
 11. The reciprocating piston machine of claim 10 wherein aplurality of gear teeth are disposed on the inner surface of the rotorand a plurality of gear teeth are disposed on the outer surface of thestator, the gear teeth of the stator being interengaged with the gearteeth of the rotor.
 12. The reciprocating piston machine of claim 9wherein when said driving force is transmitted between the rotor and thestator, and the connection between the rotor and the rotary shaft permitrelative rotation therebetween so that the rotor and the rotary shaftare capable of rotating at different speeds.
 13. The reciprocatingpiston machine of claim 9 wherein the stator and the rotor have acylindrical shape.
 14. The reciprocating piston machine of claim 9wherein the stator has an elliptical or a substantially triangular shapeand the rotor has a cylindrical or a substantially triangular shape. 15.The reciprocating piston machine of claim 9 wherein the eccentric motionprofile of the crank pin has an epi-trochoid trajectory or a hybridepi-trochoid trajectory.
 16. A machine in the form of an internalcombustion engine comprising: a stator; a rotary shaft having aneccentric journal and an axis of rotation; a rotor carried by theeccentric journal of the rotary shaft such that rotary motion istransferred between the rotor and the rotary shaft, the rotor beingconnected to the stator for communicating a driving force therebetween;a crank pin carried by the rotor, the crank pin having an eccentricmotion profile relative to the axis-of the rotary shaft when the rotoris driven by the connection between the rotor and stator; areciprocating piston; and a connecting rod having one end and an otherend, the piston being carried on the one end and the other end beingconcentrically journaled on the crank pin such that motion iscommunicated between the piston and the rotary shaft.
 17. A machineaccording to claim 16 which is of the multi-cylinder type.
 18. A machineas claimed in claim 17 comprising at least two crank pins.